Heretofore when it was necessary to have conference calls on telephones where several parties talk to each other, this was normally accomplished through using a plurality of conventional audio signals which are fed through a summing circuit to be combined into a resulting audio signal. This resulting audio signal, in turn, was fed to the headset of a receiver. While such has been satisfactory for a limited number of parties used on the conference call, it has not been practical for large conferences which would consist of several hundred parties involved. The reason for this is the degradation of the signal to noise ratio. In order to overcome this problem, devices have been developed which utilize digital signals in transmitting conference calls.
Digitized voice data, classically 12 or 13 bits of resolution, is "companded" to 8 bits for transmission in band width limited networks. Several algorithms are commercially used to perform the "companding" function, however regardless of the exact transformation function used, the eight bit result is a floating point number--i.e. mantissa plus exponent.
To operate on such numbers, (add, subtract, multiply, divide) classically the eight bit quantity is expanded to its linear form (i.e. 12 or 13 bits) prior to the operation, and then reconverted to companded form after the operation. Both of these conversions are usually performed via "look up" techniques using ROMS (Read Only Memories) or PLA's (Programmable Logic Arrays).